A large data set of ground-velocity time histories from earthquakes that occurred in Friuli-Venezia Giulia (northeastern Italy) was used to define regional predictive relationships for ground motion, in the 0.25- to 14.0-Hz frequency band. The bulk of the data set was provided by the seismic network run by Centro Ricerche Sismologiche (CRS), a department of the Istituto Nazionale di Oceanografia e Geofisica (OGS). A collection of 17,238 selected recordings from 1753 earthquakes was compiled for the years 1995–1998, with magnitudes ranging from Mw ∼1 to 5.6. Ninety-six three-component strong-motion waveforms belonging to the largest events of the 1976–1977 Friuli seismic sequence were also taken from the enea-enel accelerogram database and included in our data set. For the strongest event, which occurred on 6 May 1976 at 20:00 local time, an average local magnitude ML 6.6 was computed by Bonamassa and Rovelli (1986). The inclusion of a large number of acceleration time histories from this earthquake and six others, from magnitudes from Mw 5.2 to magnitude Ms 6.1 (three of them of Ms ∼6.0), extends the validity of the predictive relationships proposed in this study up to the highest magnitude ever recorded in the region.
Predictions for peak ground acceleration (PGA) and pseudo–spectral velocity (PSV) (5% damping) were computed through the use of the random vibration theory (RVT), with the parameters obtained from the regressions of this study.